Mobile NMO Plastic Roof ground plane

[Chevyman22360]

I have a tractor that has a NMO antenna factory install into a plastic roof. From the factory has a like tin foil under the plastic of the cab, I took a piece of heavy tin about 12x12 under the plastic roof. Reception is not very good. Wondering if there is a way to get better results. I have a pickup with a steel roof, using the same antenna and getting very good reception to what I want to listen too. Just looking for any suggestions. Thanks

 

[SteveC0625]

I have a tractor that has a NMO antenna factory install into a plastic roof. From the factory has a like tin foil under the plastic of the cab, I took a piece of heavy tin about 12x12 under the plastic roof. Reception is not very good. Wondering if there is a way to get better results. I have a pickup with a steel roof, using the same antenna and getting very good reception to what I want to listen too. Just looking for any suggestions. Thanks

What frequency range? If it's VHF, you need a larger ground plane. 17" radius or so. You can use a lighter material like metal window screening or even chicken wire fencing. As long as it makes good contact with the ground side of the body of the NMO.

Again, you did not specify what type of antenna. Accurate info generates accurate and useful answers. So I am guessing here, but... Given that it's a plastic or fiberglass roof of some kind, it probably needs a thick surface NMO mount. You will have to verify that the antenna center conductor is making good contact with the NMO center connector AND, verify that there is good continuity of the coax from the radio connector to the NMO. Check both with the antenna unplugged from the radio.

 

[Chevyman22360]

What frequency range? If it's VHF, you need a larger ground plane. 17" radius or so. You can use a lighter material like metal window screening or even chicken wire fencing. As long as it makes good contact with the ground side of the body of the NMO.

Again, you did not specify what type of antenna. Accurate info generates accurate and useful answers. So I am guessing here, but... Given that it's a plastic or fiberglass roof of some kind, it probably needs a thick surface NMO mount. You will have to verify that the antenna center conductor is making good contact with the NMO center connector AND, verify that there is good continuity of the coax from the radio connector to the NMO. Check both with the antenna unplugged from the radio.

Mainly high vhf. Trying to monitor the South Dakota digital radio system which is in the 150-170 MHz. I am using around a 16" antenna tuned for that frequency range.

 

[SteveC0625]

Mainly high vhf. Trying to monitor the South Dakota digital radio system which is in the 150-170 MHz. I am using around a 16" antenna tuned for that frequency range.

A larger ground plane will help a little, but it should not matter so much on receive only.

Like I said, verify continuity of the coax center and shield, and make sure the center contact of the NMO is firmly contacting the antenna. Use a multimeter if you can and test from the center pin of the connector at the radio end all the way to the antenna itself. Then text the shield side of the connector to ground.

If you aren't hearing them well in the tractor and do hear them well in the truck, then the antenna not electrically connected to the radio is the most obvious possible issue. Secondarily, the antenna needs to not be connected to ground, so a short to ground is the next possible issue.

 

[lmrtek]

a 1/2 wave design antenna would be a better choice

They work well without a groundplane